Thai authorities have confirmed that two cases of babies with microcephaly were caused by the Zika virus - marking the first time the link has been made in south-east Asia.
A World Health Organisation statement urged countries in the region to take stronger measures to contain the virus after Thai health officials announced the linkage was confirmed in two of three cases of babies afflicted with microcephaly (abnormally small heads).
The UN agency had earlier said the cases, if confirmed, would be the first of Zika-associated microcephaly in south-east Asia.
The virus causes the birth defect when pregnant mothers are infected.
The disease is most widely spread by mosquitoes, and the WHO is urging private citizens as well as governments to take strict mosquito control measures.